A family of Microsoft relational database management systems designed for ease of use.
MS still defaults all Office installations to 32 bit versions, even if you have 64 bit WIndows and other 64 bit Office applications already installed. Unfortunately setup.exe is too stupid to recognize the problem and simply switch to installing 64 bit ... Setup.exe in the root directory is the 32 bit installer. On your disk, look for the 64 bit folder (you mentioned one), go into it, find and run the setup program there.
MS still defaults to 32 bit because they, like many other software makers have been too lazy (aka cheap!) to update all of their addon tools to run in 64 bit.